FIG. 1 (Prior Art) is a cross-sectional diagram of a conventional conductive plug-type antifuse 110 as disclosed in U.S. Pat. No. 5,308,795. A first conductor 114 is disposed on an insulating underlying layer 112. First metal conductor 114 may comprise a sandwich structure of a lower barrier metal layer (for example, TiW), an aluminum layer (for example, AlSiCu), and an upper barrier layer (for example, TiW). Layer 116 is a layer of dielectric (for example, PECVD silicon dioxide). A conductive plug is disposed in an opening 118 in layer 116 and includes a conductive material 120 (for example, TiW) and a planarizing material 122 (for example, spin-on glass). Layer 124 is a layer of antifuse material (for example, a single layer of amorphous silicon). A capping layer 126 (for example, TiW or TiN) is provided on antifuse material layer 124 to prevent contamination of the antifuse layer from atoms in an overlying second metal conductor. Oxide spacers 128 are provided in order to minimize step coverage problems for the overlying second metal conductor 130.
When unprogrammed, the first conductor 114 is not coupled to the second conductor 130 through the antifuse 110. When programmed, however, antifuse 110 forms a permanent electrical connection between the first conductor 114 and the second conductor 130.
It is desired to improve such an antifuse.
A metal-to-metal conductive plug-type antifuse has a conductive plug disposed in an opening in an insulating layer. A layer of a programmable material (for example, amorphous silicon) overlies the conductive plug. A conductor involving a metal (for example, aluminum or copper) that migrates in the programmable material overlies the programmable material. The antifuse is programmed by forming a connection through the layer of programmable material such that the conductive plug is connected to the overlying conductor.
To prevent migration of metal from the conductor into the programmable material when the antifuse is not programmed, the conductor has a layer of barrier metal between the metal that migrates and the programmable material. In some embodiments, there are two layers of barrier metal. An airbreak after formation of the first barrier metal layer causes an improvement in the barrier properties of the first barrier metal layer. This airbreak may cause grain boundaries in the upper surface of the first barrier metal layer to be stuffed and/or may cause the upper barrier metal layer to be formed with different grains or a different grain orientation than the lower barrier metal layer. In some embodiments, a capping layer over the top surface of the programmable material protects the underlying programmable material during an ashing step when a mask used to etch the programmable material is removed. The capping layer and the programmable material form a capping layer/programmable material layer stack within the antifuse underneath the two barrier metal layers. The capping layer may also be made of a barrier metal and constitute an additional barrier.
This summary does not purport to define the invention. The invention is defined by the claims.